Growth disorders and reproductive disorders occur in plants outside their normal growth temperatures, which are different depending on the plants, and the plants are placed under extremely disadvantageous condition against species preservation (i.e., high stress condition). Therefore, plants have mechanisms to adapt to high and low temperature stresses by inducing the expressions of specific genes in response to these stresses (Naoki Sato, Tissue Culture, 19: 357 (1993); Thowashou M, Adv. Genet., 28: 99; (1990)). As to cold stress, in many cases, it takes a long time, such as several days, for plants to induce stress genes, as reported in the literature (Koga-ban Y, Abe M, and Kitagawa Y Plant Cell Physiol., 32: 901–905 (1991)).
Cytoplasmic calcium ions are recognized as second messengers for endogenous and environmental signaling in plants and animals. In plants, an increase in cytoplasmic calcium ions is caused by hormones such as auxin and abscisic acid, by non-biological environmental signals such as cold stress and mechanical stress, and by biological signals involved in recognition of commensals and pathogens.
In animals, calreticulin (CRT), which is a calcium binding protein, functions as a multi-functional regulatory factor involved in cell adhesion, maintenance of intracellular calcium homeostasis, protein folding, and environmental stress response (Kwor M S, Park C S, Choi K, Ahnn J, Kim J I, Eom S H, Kaujiman S J, and Song W K, Mol. Biol. Cell 11: 1433–1443 (2000)). It has already been confirmed that CRP55, Calregulin, HACBP, ERP60, CALBP, and CaBP3 are members of the CRT class. Rice CRT was cloned and is known to be involved in suppressing redifferentiation rate of rice callus and in regulating rice stem and leaf elongation (Li Z, Komatsu S, Eur. J. Biochem., 267: 737–745 (2002)). However, its molecular mechanism has not been well characterized.